Heating, ventilation and air conditioning (HVAC) systems are employed to control the air flow and temperature in the occupant's compartment of a motor vehicle. In a typical system, a heater core is operatively connected to the radiator of an internal combustion engine and an air conditioning evaporator core is operatively connected to the condenser and other components of the air conditioning system. Generally, the heater and evaporator cores are separate heat exchanger units and are located at spaced locations in a modular housing for the HVAC system so the temperature of air entering into the passenger compartment can be readily changed by varying the distribution of air flow through the heater and evaporator cores by adjusting the position of air flow control baffles and doors fitted inside the modular housing. While such systems are highly effective and operate with good efficiency, they require considerable space and large modular housings that are mounted in crowded compartments such as that for the vehicle engine. Since such cores are completely separate from one another, more material, labor effort, and space is required, and overall vehicle weight is increased.
In the HVAC system, the evaporator cools, dries and cleans the air that enters the passenger compartment. In operation, a refrigerant enters the evaporator as a low pressure mixture of liquid and vapor. The liquid vaporizes at the low pressure, absorbing large quantities of heat from the passing air. As the heat is transferred through the walls of the evaporator from the air passing over it, moisture in the air condenses on the surface and is drained off, carrying foreign materials such as dust and pollen.
The engine coolant system includes a closed system for coolant flow. The prime function of the engine cooling system is to dissipate heat generated by the combustion of fuels in the combustion chambers of the engine to maintain engine temperature at a specified level under anticipated operating conditions. Usually there are two heat exchangers in the cooling system of a vehicle: (1) a radiator for dissipating excessive heat energy generated by engine operation, and (2) a heater to transfer heat energy to air delivered to the passenger compartment.
In vehicle HVAC systems, separate evaporator and heater cores may be assembled into a common case. Depending upon the location of the heater with respect to the evaporator, there are two air-mix temperature control designs, namely series air mix and parallel air mix. The series air mix utilizes the evaporator core upstream of the air supply and the heater core offset within the air flow such that all inlet air is directed through the evaporator core, and thereafter selectively directed through the heater core. When the compressor is turned on, the air is cooled and dehumidified. Otherwise, air passes unchanged through the evaporator. A blend door can divert a variable portion of the air through the heater core. These two air streams are then mixed and delivered to the air distribution system. In the parallel air mix system, separate evaporator and heater cores are located end-to-end. The evaporator and heater are in parallel air paths and the blend door varies the amount of air passing through each. At full cold setting, all air passes through the evaporator and none through the heater. At full hot setting, all air passes through the heater and none of the air passes through the evaporator. At intermediate settings, a portion of the air stream passes through the heater and evaporator.
An integrated heater-evaporator core can meet the functional requirements for both of the air mix systems described above. However, the present invention is particularly suitable for the parallel air mix since its geometry readily fits the available space in a wide range HVAC housings.
The above heat exchangers generally may be of the U-flow tube and fin type, such as disclosed in my U.S. Pat. No. 5,058,662 for TUBE END SUPPORT FOR U-CHANNEL EVAPORATORS assigned to the assignee of this application and hereby incorporated by reference, which discloses heat exchanger utilizing pairs of plates forming tube passes and tanks wherein a plurality of the tubes are layered or stacked with fin type air centers therebetween to form the heat exchanger. The pair of tanks are formed by interconnected drawn cups located at one end of the tubes and are interconnected by the U-channels thereof.